The Computing Landscape of the 21st Century

This paper shows how today's complex computing landscape can be understood in simple terms through a 4-tier model. Each tier represents a distinct and stable set of design constraints that dominate attention at that tier. There are typically many alternative implementations of hardware and software at each tier, but all of them are subject to the same set of design constraints. We discuss how this simple and compact framework has explanatory power and predictive value in reasoning about system design.